The present invention relates to a filter element which is precoated with kieselguhr or the like auxiliary filtering agent and highly adapted for execution of filtration of beer or the like liquid.
In the conventional production step of beer, Japanese sake and the like, such filtering apparatuses as using kieselguhr and the like auxiliary filtration agent for execution of clarifying filtration are broadly employed.
As for the filter elements serving for this purpose, the filter element per se is porous and thus serving for filtering function, and in addition, the outer surface thereof acts as mounting means for the precoated kieselguhr or the like auxiliary filtering agent, thus providing a combined filtering function together with the auxiliary filtration agent.
As such kind of porous filter element, porous cylindrical ceramic filters were disclosed as an example in Japanese Patent Publication No. 18986/1984.
These known porous cylindrical ceramic filters which act as mounting means for a precoat layer of kieselguhr or the like auxiliary filtering agent are superior in such a point as having a higher rigidity of the filter element per se in comparison with conventional wire mesh mode filter elements, thereby minimizing disadvantageous deformation and vibration otherwise caused by fluctuation in pressure and liquid flow rate frequently appearing in and through the filter vessel. More specifically, when the filter elements are used in beer-manufacturing plants, even if fluid pressure and flow rate fluctuations of the above-mentioned nature frequently occur, thus inviting disadvantageous crackings in the precoating layers, beer yiest and impurities are not apt to leak therethrough into the purified beer.
However, it should be noted that the conventionally used porous cylindrical ceramic filter of the above kind has generally a rather thick wall, amounting to 20.about.30 mm, and especially by virtue of the porous structure, and thus, when a reverse flow cleaning step is applied, in advance of applying a precoating of auxiliary filtering agent, it is highly difficult to remove residual kieselguhr and organic impurities clogged in the fine pores, thereby liably inviting clogging of the filtering pores. For avoiding such stop-pore phenomenon, at least once a year a regenerating treatment must be carried out disadvantageously.
Since the conventional filter elements are made of ceramic material, and thus, the hardness shows a higher value, but the material is naturally brittle so that mechanical damages such as surface cracking and breakage may frequently occur during operator's ill-treatment and/or collision against other hard substance, which means naturally a grave problem to be solved out.
As is commonly known, in the case of ceramic filters, it is highly difficult to produce a large length one. Thus, it is the conventional technique to fusingly joint certain commonly available length ceramic tubes one after another or to introduce gasket means between a pair of neighboring short length ceramic tubes and then the total elongated assembly is mechanically fixed longitudinally and under pressure by means of a fixture or the like, for attaining a desirously elongated tubing. In the case of the elongated filter element manufactured with use of fusingly jointing agent, it is observed that the latter is liably subjected to corrosion by contact with alkaline cleaning solution as commonly used in the beer manufacturing line for sterilizingly cleaning purpose. For avoiding such trouble as set forth above, it was necessary to use chlorine-containing cleaner solution for execution of a separate line cleaning job on the beer manufacturing line including the ceramic-made filter element(s) and independent of conventionally employed line cleaning job. On the other hand, in the case of the mechanically conjoined filter element above set forth, the structure thereof is rather complicated and the manufacturing cost is considerably high.